1. Field of the Invention
The present invention relates to a suspension system for an automotive vehicle so adapted as to control the posture of an automotive vehicle body by controlling the supply or discharge of a fluid to or from a cylinder and, more particularly, to a suspension system for the automotive vehicle involved particularly with fail safe measures in the event of an incident in a supply-discharge control system.
2. Description of Related Art
A suspension system for the automotive vehicle is known, for example, as disclosed in Japanese Patent Laid-open Publication (kokai) No. 130,418/1988, which has plural cylinders disposed between a spring weight and an unsprung weight for each wheel, to each of which plural gas springs are connected so as to allow the independent and separate supply or discharge of the fluid to each cylinder, thereby performing the control over the posture of the automotive vehicle body. This system is known as an active control suspension system (ACS system).
For such an ACS system, a supply-discharge control valve for supplying or discharging an operating fluid is so arranged as to be controlled by supply or discharge control means under a predetermined condition. It is to be noted, however, that an incident may be caused to occur to such an extent that the supply-discharge control means cannot work in a correct way. Such an incident is considered to include incidents with respect to the supply-discharge control means itself as well as various sensors, fluid circuits for supplying or discharging the fluid, among many others. When those incidents occur, the posture of the automotive vehicle body cannot be controlled in a normal way so that the control by the supply-discharge control means should be suspended.
It is to be noted herein that, when the supply or discharge control means is suspended while the automotive vehicle is cornering, the automotive vehicle body is kept learning (rolling) even if the automotive vehicle body is returned to the straight running state. In other words, while the automotive vehicle body is cornering, transverse acceleration acts upon the automotive vehicle body as centrifugal force, thereby causing the automotive vehicle body to lean in the direction in which the transverse acceleration works and imposing different loads onto the left-hand and right-hand wheels. The ACS system is so designed as to control the different loads disposed upon the left-hand and right-hand wheels by changing inner pressures within the respective cylinders for the left-hand and right-hand wheels. However, a new problem may arise when the control by the supply or discharge control means is suspended, which involves leaning the automotive vehicle body in the opposite direction when the automotive vehicle body is returned to its straight running state from the cornering state by acting the different loads upon the left-hand and right-hand wheels.